using System;
using System.Diagnostics;
using System.Threading;

namespace CS_SQLite3
{
  public partial class CSSQLite
  {
    /*
    ** 2007 August 14
    **
    ** The author disclaims copyright to this source code.  In place of
    ** a legal notice, here is a blessing:
    **
    **    May you do good and not evil.
    **    May you find forgiveness for yourself and forgive others.
    **    May you share freely, never taking more than you give.
    **
    *************************************************************************
    ** This file contains the C functions that implement mutexes for win32
    **
    ** $Id: mutex_w32.c,v 1.18 2009/08/10 03:23:21 shane Exp $
    **
    *************************************************************************
    **  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
    **  C#-SQLite is an independent reimplementation of the SQLite software library
    **
    **  $Header$
    *************************************************************************
    */
    //#include "sqliteInt.h"

    /*
    ** The code in this file is only used if we are compiling multithreaded
    ** on a win32 system.
    */
#if SQLITE_MUTEX_W32


/*
** Each recursive mutex is an instance of the following structure.
*/
struct sqlite3_mutex {
CRITICAL_SECTION mutex;    /* Mutex controlling the lock */
int id;                    /* Mutex type */
int nRef;                  /* Number of enterances */
DWORD owner;               /* Thread holding this mutex */
};

/*
** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
** or WinCE.  Return false (zero) for Win95, Win98, or WinME.
**
** Here is an interesting observation:  Win95, Win98, and WinME lack
** the LockFileEx() API.  But we can still statically link against that
** API as long as we don't call it win running Win95/98/ME.  A call to
** this routine is used to determine if the host is Win95/98/ME or
** WinNT/2K/XP so that we will know whether or not we can safely call
** the LockFileEx() API.
**
** mutexIsNT() is only used for the TryEnterCriticalSection() API call,
** which is only available if your application was compiled with
** _WIN32_WINNT defined to a value >= 0x0400.  Currently, the only
** call to TryEnterCriticalSection() is #ifdef'ed out, so #if
** this out as well.
*/
#if FALSE
#if SQLITE_OS_WINCE
//# define mutexIsNT()  (1)
#else
static int mutexIsNT(void){
static int osType = 0;
if( osType==0 ){
OSVERSIONINFO sInfo;
sInfo.dwOSVersionInfoSize = sizeof(sInfo);
GetVersionEx(&sInfo);
osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
}
return osType==2;
}
#endif //* SQLITE_OS_WINCE */
#endif

#if SQLITE_DEBUG
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside Debug.Assert() statements.
*/
static int winMutexHeld(sqlite3_mutex p){
return p.nRef!=0 && p.owner==GetCurrentThreadId();
}
static int winMutexNotheld(sqlite3_mutex p){
return p.nRef==0 || p.owner!=GetCurrentThreadId();
}
#endif


/*
** Initialize and deinitialize the mutex subsystem.
*/
static sqlite3_mutex winMutex_staticMutexes[6];
static int winMutex_isInit = 0;
/* As winMutexInit() and winMutexEnd() are called as part
** of the sqlite3_initialize and sqlite3_shutdown()
** processing, the "interlocked" magic is probably not
** strictly necessary.
*/
static long winMutex_lock = 0;

static int winMutexInit(void){
/* The first to increment to 1 does actual initialization */
if( InterlockedCompareExchange(winMutex_lock, 1, 0)==0 ){
int i;
for(i=0; i<sizeof(winMutex_staticMutexes)/sizeof(winMutex_staticMutexes[0]); i++){
InitializeCriticalSection(&winMutex_staticMutexes[i].mutex);
}
winMutex_isInit = 1;
}else{
/* Someone else is in the process of initing the static mutexes */
while( !winMutex_isInit ){
Sleep(1);
}
}
return SQLITE_OK;
}

static int winMutexEnd(void){
/* The first to decrement to 0 does actual shutdown
** (which should be the last to shutdown.) */
if( InterlockedCompareExchange(winMutex_lock, 0, 1)==1 ){
if( winMutex_isInit==1 ){
int i;
for(i=0; i<sizeof(winMutex_staticMutexes)/sizeof(winMutex_staticMutexes[0]); i++){
DeleteCriticalSection(&winMutex_staticMutexes[i].mutex);
}
winMutex_isInit = 0;
}
}
return SQLITE_OK;
}

/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated.  SQLite
** will unwind its stack and return an error.  The argument
** to sqlite3_mutex_alloc() is one of these integer constants:
**
** <ul>
** <li>  SQLITE_MUTEX_FAST               0
** <li>  SQLITE_MUTEX_RECURSIVE          1
** <li>  SQLITE_MUTEX_STATIC_MASTER      2
** <li>  SQLITE_MUTEX_STATIC_MEM         3
** <li>  SQLITE_MUTEX_STATIC_PRNG        4
** </ul>
**
** The first two constants cause sqlite3_mutex_alloc() to create
** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
** The mutex implementation does not need to make a distinction
** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to.  But SQLite will only request a recursive mutex in
** cases where it really needs one.  If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** The other allowed parameters to sqlite3_mutex_alloc() each return
** a pointer to a static preexisting mutex.  Three static mutexes are
** used by the current version of SQLite.  Future versions of SQLite
** may add additional static mutexes.  Static mutexes are for internal
** use by SQLite only.  Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
** returns a different mutex on every call.  But for the static
** mutex types, the same mutex is returned on every call that has
** the same type number.
*/
static sqlite3_mutex *winMutexAlloc(int iType){
sqlite3_mutex p;

switch( iType ){
case SQLITE_MUTEX_FAST:
case SQLITE_MUTEX_RECURSIVE: {
p = sqlite3MallocZero( sizeof(*p) );
if( p ){
p.id = iType;
InitializeCriticalSection(p.mutex);
}
break;
}
default: {
Debug.Assert( winMutex_isInit==1 );
Debug.Assert(iType-2 >= 0 );
assert( iType-2 < sizeof(winMutex_staticMutexes)/sizeof(winMutex_staticMutexes[0]) );
p = &winMutex_staticMutexes[iType-2];
p.id = iType;
break;
}
}
return p;
}


/*
** This routine deallocates a previously
** allocated mutex.  SQLite is careful to deallocate every
** mutex that it allocates.
*/
static void winMutexFree(sqlite3_mutex p){
Debug.Assert(p );
Debug.Assert(p.nRef==0 );
Debug.Assert(p.id==SQLITE_MUTEX_FAST || p.id==SQLITE_MUTEX_RECURSIVE );
DeleteCriticalSection(p.mutex);
//sqlite3DbFree(db,p);
}

/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
static void winMutexEnter(sqlite3_mutex p){
Debug.Assert(p.id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
EnterCriticalSection(p.mutex);
p.owner = GetCurrentThreadId();
p.nRef++;
}
static int winMutexTry(sqlite3_mutex p){
int rc = SQLITE_BUSY;
Debug.Assert(p.id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
/*
** The sqlite3_mutex_try() routine is very rarely used, and when it
** is used it is merely an optimization.  So it is OK for it to always
** fail.
**
** The TryEnterCriticalSection() interface is only available on WinNT.
** And some windows compilers complain if you try to use it without
** first doing some #defines that prevent SQLite from building on Win98.
** For that reason, we will omit this optimization for now.  See
** ticket #2685.
*/
#if FALSE
if( mutexIsNT() && TryEnterCriticalSection(p.mutex) ){
p.owner = GetCurrentThreadId();
p.nRef++;
rc = SQLITE_OK;
}
#else
UNUSED_PARAMETER(p);
#endif
return rc;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
static void winMutexLeave(sqlite3_mutex p){
Debug.Assert(p.nRef>0 );
Debug.Assert(p.owner==GetCurrentThreadId() );
p.nRef--;
Debug.Assert(p.nRef==0 || p.id==SQLITE_MUTEX_RECURSIVE );
LeaveCriticalSection(p.mutex);
}

sqlite3_mutex_methods *sqlite3DefaultMutex(void){
static sqlite3_mutex_methods sMutex = {
winMutexInit,
winMutexEnd,
winMutexAlloc,
winMutexFree,
winMutexEnter,
winMutexTry,
winMutexLeave,
#if SQLITE_DEBUG
winMutexHeld,
winMutexNotheld
#else
null,
null
#endif
};

return &sMutex;
}
#endif // * SQLITE_MUTEX_W32 */
  }
}

